U.S. Pat. No. 4,455,543 describes an electromagnetic actuator for operating a cylinder valve in an internal-combustion engine. The actuator essentially is formed of two spaced electromagnets wherein the pole faces of one electromagnet are oriented towards the pole faces of the other electromagnet. In the space defined between the pole faces of the two electromagnets an armature is disposed which is coupled with the cylinder valve and which, dependent upon the alternating energization of the electromagnets, moves back and forth against the force of resetting springs. In the respective terminal position of the cylinder valve (open or closed position) the armature is in engagement with the pole face of the respective holding magnet and is maintained there as long as the holding electromagnet is in an energized state. In the position of rest the armature is in a mid position between the pole faces of the two electromagnets, determined by the force equilibrium of the two oppositely working resetting springs.
If, during operation, the armature is to be displaced from one of its end positions into the other, the holding electromagnet is de-energized so that the armature, together with the cylinder valve, is moved by the force of the associated return spring in the direction of the mid position (position of rest). Upon subsequent energization of the opposite, capturing electromagnet, the armature will be in the effective range of the magnetic field of the capturing electromagnet and is moved by means of the magnetic force against the force of the other return spring into the other end position. As the armature impacts on the pole face of the capturing electromagnet, noise is generated whose intensity is dependent from the magnitude of the impact velocity. At the same time, risks are high that the armature rebounds which, for example, upon closing the cylinder valve, may lead to a brief reopening of the valve after the latter has already been seated. By a suitable control of the energization of the momentarily capturing electromagnet it is feasible to reduce the impact velocity; yet, the impact velocity has to be at all times sufficiently high to ensure that the armature is securely captured, that is, it securely arrives into engagement with the pole face.
To minimize the unavoidable impact noises, an impact velocity of approximately 0.02 m/s is required for the armature in electromagnetic valve drives of the above-outlined type. Such low impact velocities have to be ensured in all real operating conditions while taking into consideration all related stochastic fluctuations; this, however, requires a substantial circuitry outlay. In vehicle engines irregularities in the road surface or other effects in the terminal approaching phase of the armature are sufficient to cause a sudden drop of the armature in case the magnetic force is oriented precisely in the direction of force requirement which is necessary for such a minimum impact velocity. A residual noise, however, cannot be avoided.